A drone (y.1) comprises an airframe and multiple arms (b) that are attached to the airframe with a motor and rotor (j) attached to each of the arms (b) at a position remote from the airframe. Some, but preferably all of the arms (b) are pivotally attached to the airframe, to pivot relative to the airframe from an operational position of the arm (b) in a deflection direction and each arm (b) has a bias element (c, d, R) that is configured to bias the arm (b) to pivot in a return direction that is opposite to its deflection direction, to return the arm (b) to its operational position.